Draft control for fuel burners



Dec. 20, 1938. w. w. PECK 2,140,761

DRAFT CONTROL FOR FUEL BURNERS Filed Aug. 26', 1955 2 SheetsSheet l Dec. 20, 1938.

W. W. PECK v DRAFT CONTROL FOR FUEL BURNERS 2 Sheets-Sheet 2 Filed Aug. 26, 1935 Patented Dec. 20, 1938 UNITED STATES PATENT OFFICE 1 Claim.

This invention has to do with fuel combustion apparatus, and relates more particularly to a draft control therefor.

Ordinarily, furnaces supplied with fuel by an automatic stoking means have separate passages for the introduction of fuel and air. While the furnace is being operated a gas pressure builds up in the combustion retort, as a consequence of which combustible gases are frequently forced backwardly through the fuel injector passage and into the fuel hopper, from which they may escape into the atmosphere. In addition to the wasteful loss of combustible gases so escaping from the furnace, there is the undesirable factor of the gases being unhealthful to a person who may breathe them.

One method that has been employed to prevent the escape of gases from mechanically fired furnaces consists of diverting a portion of the air draft into the fire box by way of the fuel injector tube. This mode of firing proves quite satisfactory so long as the fire bed develops no blow holes. When, however, an opening is formed in the fire bed, the draft through the draft passage accelerates rapidly thereby increasing the pressure within the fire box and thus forcing a portion of the unburned gases and smoke backwardly through the fuel injector tube and into the stoker or hopper. Such backward flow of gas through the fuel injector tube is possible because there is no increase in pressure at the intake end of the fuel injector passage concurrently with the building up of pressure in the fire box. There is, therefore, efiected an overbalancing of pressures at the two ends of the fuel injector passage and a consequential reversal in the flow of gas within the passage.

Passage of unburned gas from the fire box of the furnace by way of the fuel injector passage into the fuel hopper and thence outwardly into the atmosphere has been prevented by sealing the hopper of the stoker. This method of firing is objectionable because the hopper cover must be maintained sealed during operation of the apparatus. Furthermore, during-the operation of the apparatus there is a gradual accumulation of the injurious unburned gases in the hopper so that at any subsequent time when the cover is removed much of the gas will escape.

Among the objects of the present invention is the provision of:

A stoker of s mplified construction adapted to prevent the escape of gases from' the furnace used in combination therewith. and without encountering any of the objectionable features enumerated above and had by contemporary stokers;

An improved stoker including an accumulator for gases tending to escape from the furnace and means for introducing the gases from the accumulator into the furnace air intake passage;

A new draft control apparatus including a novel damper device self-regulated in accordance with the demand for draft through a passage in which it is disposed;

An improved unitary damper device regulatable for effecting a predetermined natural draft and a predetermined forced draft.

With the above and other desirable objects in view, the description of the device is hereinafter set forth with reference to the two sheets of drawings hereby made a part of this specification, and in which:

Fig. 1 is a side elevation of an embodiment of the present invention, there being sections broken away to facilitate illustration of construction details;

Fig. 2 is a fragmentary sectional view of the device taken on the line 2-2 of Fig. 1 and showing the construction of an improved damper device;

Fig. 3 is a plan view of the apparatus shown in Fig. 1, with parts thereof broken away; and

Fig. 4 is a fragmentary sectional view of the device taken on line 4-4 of Fig. 3.

Like numerals of reference are used for designating the same parts of the device illustrated in the various figures of the drawings and described hereinafter.

Referring first to Fig. 1, there will be seen a stoker designated generally by the reference character I 0. The stoker I0 is for use in combination with a furnace and retort l I of which the fire box Ila is shown in Fig. 4. Within the stoker Ill, which may be contained in a housing constructed of sheet metal, is a hopper l2 for fuel such as small lump coal and screenings. Enclosed within a front compartment l3 of the stoker I0 is a prime mover M which has suitable driving connections with a draft fan l5 enclosed within a casing I 6, and with a screw l1 disposed within a fuel passage l8. The prime mover l4 for energizing the illustrated form of the invention is an electric motor which may have remotely controlled starting mechanism enclosed within a box Ha.

A shaft l9, shown in Fig. 2, forms a part of the driving connection between the prime mover l4 and the draft fan IS. The fan 15 includes a flanged hub member 20 secured nonrotatively to the shaft l9 by a key 2|. A set screw 22 prevents axial movement of the hub 20 relative to the shaft l9. Carried upon the flanged portion of the hub 20 is an annular framepiece 23 to which is secured the ends of a series of fan blades 24. The opposite ends of the fan blades 24 are fastened to an opposed annular piece 25. The lower portion 26 of the fan casing I6 has connected thereto an air discharge tube 2! which leads to the retort II. This construction is plainly shown in Figs. 1, 2 and 3.

A circular opening 28 is formed in the outer wall of the fan casing I6. Circumscribing the opening 28 is a rabbeted portion 29 of the casing l6 into which there is fitted a slightly coniform ring 30, formed of sheet material having a central opening 3|. The ring 30 is retained in the fan, casing wall by means of an expanding fit into the bezel 29; the ring may be forced into the wall section by hammering or by a pressing operation. An upper portion of the ring member 30 contains a notch 32. Extending across the notch is a pivot pin 33, the pin being suitably anchored to the ring 3|! on opposite sides of the notch. Pivotally depending from the pin 33 is a substantially circular damper member 34 having a tongue 35 extending upwardly in spaced relation with the inner face of the ring 30. The base portion of the tongue 35 is undulated to adapt it to hook over and about the pin 33. The damper 34 hangs from the pin 33 and is easily swung thereabout between positions interiorly and exteriorly of the opening 3|. Normally, the damper 34 will hang in the position shown in full outline in Fig. 2. Such normal position, however, may be regulated by changing the center of gravity of the damper pursuant to changing the axial position of a threaded weight member 36 relatively thereto. The adjustable weight is disposed within a threaded aperture 36a arranged centrally of the damper. Pivotal movement of the damper member 34,inwardly of the housing I6 is adjustably limited by a bolt 31 anchored within the ring 30 in registry with the tongue 35. Any selected position of the bolt 31 may be maintained by means of a locking nut 38. The bolt or stop 31 cooperates with the damper member 34 during such times as a forced draft is being drawn through the opening 3| in a manner hereinafter described.

In Figs. 1, 3 and 4 there is shown a wall 39 depending into the stoker, such wall forming a section of the rear wall of the hopper and the front wall of a gas receiving compartment. While there is a combustion of fuel in the fire box Ila,

there isa tendency for smoke and gas to be forced downwardly and backwardly through the fuel injector tube 3 along the course indicated by the arrows in Fig. 4. The gas escaping in this manner has a tendency to followthe upper section of the fuel injector tube, and to turn abruptly upwardly upon reaching the end of the tube connected to the stoker. after referred to as the gas receiver, formed between the wall 39 and the adjacent end wall section 40 of the stoker serves as a receiver for the gas, and prevents its escape into the main portion .of the stoker or the hopper thereof. Means for preventing the gas receiver from filling and overflowing with such gas will now be described.

An aperture 4| is formed in a side wall of the receiver compartment between wall sections 39 and 40. A conduit 42 has one end secured to the compartment wall and communicating with the compartment through the aperture 4|. The opmember 36.

The trap, hereila position 3.

posite end of the conduit 42 has a hooded end section 43 providing a side opening 44 in close proximity to and in opposed relation to the damper member 34.

Operation of the apparatus is as follows: 5

When the motor I4 is set in motion to cause the screw member to draw fuel from the hopper l2 forinjection into the fire box Ila, the fan I5 is likewise set in motion for drawing air inwardly through the opening 3| and forcing such air through the portion 26 of the casing l6 and the air passage-21 into the retort. Upon being forced into the' retort, the air passes through openings 45 in the fire box ||a to the fire bed.

While there is a natural draft through the opening 3| and the draft passage 21 into the fire box, the damper member 34 will be drawn inwardly to a position such as position A shown in dotted outline. Upon the creation of the forced draft through the device, however, the damper member 34 will be moved inwardly of the casing l6 to a position B which is determined by the adjustment of the stop member 31 and the coaction of the latter with the tongue 35 pro- Jecting from the upper side of the damper member. Thus, the size of the draft opening is regulatable to predetermine the amount of air admitted to the fire box during forced draft thereto, and also during such time as there is a natural draft. When the device has finished the stoking operation, the motor M will cease to run, whereupon the fuel feed screw l1 and the fan l5 will stop rotating; the forced draft will cease to flow; and the damper member 34 will swing outwardly by force of gravity to the position A. Furth r outward movement of the damper member 34 is opposed and prevented by the incoming natural draft. The size of the space between the damper member 34 and the edge of opening 3| for the admission of the natural draft is regulatory by means of the threaded weight By shifting the weight 36 within the threaded aperture 360. of the damper, the center of gravity of such damper may be changed and thus vary the component of gravitatlonai force thereon opposed to the force exerted thereon by the incoming air.

Because of the air stream induced through the opening 3| into the draft passage of the device there is efiected an area of reduced pressure about the opening 44in the hood 43 forming an end of the conduit 42. This reduction in pressure will induce the fiow of gas from the receiver compartment within the stoker member into and through the conduit. It is desirable that the flow of air and gas through conduit 42 be not so great as to cause the fiow of gas backwardly through the fuel injection tube l8; that is, from the fire box through the fuel injection tube and into the so stoker. The amount of gas drawn through'the passage or conduit 42 is regulated both by the diameter or capacity of the conduit 42 and by the proximity of the end opening 44 thereof to the damper member 34. It will be conceived that the damper member 34 in addition to controlling the flow of air into the opening 3| also partially obstructs the opening 44 in the conduit 42 and regulates the amount of gas induced through the conduit. While a natural draft is passing into the device and the damper member 34 is in' the position A, there is less induction of gas through the conduit 42 than when the damper member 34 is removed from the opening 44 and in the While only a specific embodiment of the invention has been shown in the drawings and described, applicant is aware that the device may take other forms without departing from the spirit of the invention the scope of which is intended to be limited only as hereinafter set forth in the appended claim.

I claim as my invention:

A coal stoker comprising in combination, a coal retort having a combustion draft passage and a coal feed passage, a coal container connected with said coal passage and having a portion thereof adjacent to the inlet of said coal passage partitioned off to form a gas receiver, a power driven blower having its outlet connected to said combustion draft passage, a damper mechanism for the inlet of said blower, including a damper support, a damper member pivotally depending from said support obstructiveiy into the inlet of said blower and automatically adjustable about its pivotal axis to vary the degrees of obstruction of said blower inlet in response to air intake velocity, and a gas conduit having one end communicating with said gas receiver and its other end disposed for discharge of gas therefrom into the inlet of said blower on the atmospheric side of said damper, the latter end of said gas conduit being in opposed relation to said damper member and partially obstructed thereby so that movement of said damper member changes the degree of obstruction of said conduit.

WILLIAM W. PECK. 

